A bartender pours a glass of beer at Clare and Don's Beach Shack in Falls Church, Va.

ALCOHOL ABUSE, DEPENDENCE

Number of Americans 12 and older who reported either alcohol abuse or dependence:

18.6 million

Source: SAMHSA, National Survey on Drug Use and Health, 2007

By Rita Rubin, USA TODAY

You probably know people who get tipsy after a drink or two. Maybe you're one yourself.

Over the past several decades, studies of college students have shown that such individuals are one-third to one-half as likely to develop alcoholism as those who drink and drink and drink before they feel drunk.

Now scientists have identified a gene that has a "big, big effect" on how people respond to alcohol, says Kirk Wilhelmsen, senior author of a paper posted Tuesday by the journal Alcoholism: Clinical and Experimental Research. About 10% to 20% of the population carry a version of the gene that makes their brains especially sensitive to alcohol.

The finding, Wilhelmsen says, "potentially changes the paradigm about how we think about how alcohol affects the brain." While the finding doesn't yet have any treatment application, he says, "my expectation is this is actually going to lead somewhere."

The gene carries the blueprint for an enzyme called CYP2E1, known to be involved in metabolizing ethanol alcohol as well as other molecules, such as the pain-reliever acetaminophen, or Tylenol, and nicotine. People who carry the version of the CYP2E1 gene linked to increased sensitivity to alcohol produce more of the enzyme.

The CYP2E1 enzyme works in the brain, which is not the major player in alcohol metabolism, says Wilhelmsen, a genetics professor at the University of North Carolina-Chapel Hill School of Medicine. Another enzyme, in the liver, "does most of the heavy lifting" in breaking down alcohol, he says. Apparently, though, CYP2E1 affects how sensitive the brain is to alcohol, perhaps because it — unlike the enzyme in the liver — generates free radicals, tiny molecules that can damage cells.

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